Monthly Archives: January 2015

We are all familiar with the effects of epinephrine (adrenaline) and norepinephrine (noradrenaline) on us when placed in a position of stress, such as public speaking or even worse danger. We flush, shake, our heart rate accelerates and many of us we begin to sweat profusely, thus visibly advertising our distress; sometimes embarrassingly so

if we have an antiperspirant fail and happen to be wearing a dark shirt.

Those seeing these symptoms may feel a degree of sympathy for the victim, but do not usually flee the scene, although they may sometimes feel tempted to do so.

The case with aphids is very different. Aphids, when perceiving a threat to their neighbours by a predator or parasite, flee the scene rapidly, by flight, if winged, on foot if not, or even by leaping from their host-plant to the ground below. The pea aphid, Acyrthosiphon pisum walks away or drops from their plant (Clegg & Barlow, 1982) as does the rose-grain aphid, Metopolophium dirhodum (Larsen, 1988). This may seem a risky move since it seems that about 10% of all aphids that fall from their host plant don’t manage to get back (Sunderland et al., 1986), but for a clonal organism the risk is obviously worth it.

So how does this communal fright and flight response come about? Most aphids have a pair of siphunculi or cornicles at the rear of their abdomen. These vary in size and shape, in some aphids being long and slender, in others short and stubby and in yet others reduced to a shallow indentation (pore) or in a few species, totally absent.

The role of aphid siphunculi has been debated since the days of Linneaus and Reaumur who considered them to be the source of honeydew (Hottes, 1928). Hottes himself in a comprehensive review of the various theories put forward for the function of the siphunculi, dismissed the defence theory of Busgen (1891) and plumped for an excretory role, although he did suggest that volatile substances were produced by the siphunculi in addition to the waxy visible drops. By the middle of the last century it was generally accepted that the siphunculi were involved in defence, but in a purely physical way, in that the waxy exudate was used to deter or disable the attacking predators or parasites (e.g. Dixon, 1958; Edwards, 1966). At about the same time, the chemical composition of the visible exudate was confirmed as being primarily triglycerides with myristic acid being the major fatty acid present (Strong, 1966).

Hawthorn-parsley aphid Dysaphis apiifolia producing sipuncular exudates whilst under attack by a parasitic wasp. Many thanks to Tom Pope for permission to use this clip.

In 1968 an alarm pheromone was identified and isolated from the cotton stainer, Dysdercus intermedius (Calam & Youdeowei, 1968) so it was not surprising that attention should be focused on aphids, many of which show a similar group dispersive behaviour when a predator approaches them. The aphid alarm pheromone (E)-β-farnesene was, however, not formally identified until 1972 (Bowers et al, 1971), although Maria Dahl had demonstrated the previous year that a solution made from crushed aphids would cause an alarm response in other aphids of the same and different species (Dahl, 1971). Unsurprisingly, as during the 1970s and 1980s scientists from the USA were notorious for only citing papers written in English, Bowers et al. (1972), failed to cite her in their paper, instead citing two other American authors (Kislow & Edwards, 1972).

This discovery resulted in a flurry of papers from around the world as insect physiologists vied to be the first to isolate alarm pheromone from different aphid species (e.g. Weintjens et al., 1973; Montgomery & Nault, 1977; Wohlers, 1980). There were also more ecological studies such as that examining the way alarm pheromone in ant-attended aphids enhances the relationship between them and their ant farmers (Nault et al., 1976) thus acting as a synomone (Nordlund & Lewis, 1976). As time has gone on the interest in aphid alarm pheromone has remained unabated with new twists and surprises being discovered. For example, as well as stimulating the escape response, the alarm pheromone also stimulates those surviving pea aphids to produce winged offspring thus facilitating future long-distance dispersal away from the predators (Kunert et al., 2005). Aphid alarm pheromone can also act to help natural enemies find their aphid prey (e.g. Micha & Wyss, 1996), in this case acting as a kairomone.

An allomone is any chemical substance produced and released by an individual of one species that affects the behaviour of a member of another species to the benefit of the originator but not the receiver e.g. the ability of some plants to release aphid alarm pheromen and thus deter aphids form landing on them.

An apneumone is any substance produced by nonliving material that benefits a recipient species but is detrimental to a different species associated with the non-living material

A kairomone is a semiochemical, emitted by an organism, which mediates interspecific interactions in a way that benefits an individual of another species which receives it, without benefiting the emitter. For a detailed critique of the term kairomone see Ruther et al. (2002).

A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behaviour of the receiving individual e.g. alarm pheromones, food trail pheromones and sex pheromones.

A synomone is a substance produced by an individual of one species that benefits both the producer and the recipient which is of a different species. An example is the release of chemical elicitors by plants that attract entomophagous insects when they are attacked by herbivores.

They are of course, designed to do just that and so as entomologists we should be happy that they are so good at their job. The secret of their success lies in their colour, yellow, which is highly attractive to many flying insects, flies (Disney et al., 1982) and aphids (Eastop, 1955) being particularly attracted to them as are bees and wasps (Vrdoljak & Samways, 2012; Heneberg & Bogusch, 2014). They are also attractive to thrips (Thysanoptera) (Kirk, 1984) and have long been the subject of many comparative studies (e.g. Heathcote, 1957), although the prize for one of the most elaborate and labour intensive studies involving pan traps must go to my friend and former colleague Thomas Döring (Döring et al., 2009) who ran an experiment using pan traps of seventy, yes seventy, different colours! They are easy to deploy and range from expensively bought made-to-order versions to yellow plastic picnic plates, yellow washing up basins and even Petri dishes painted yellow. They can be mounted on poles and sticks or just placed on the ground; to say that they are versatile is a bit of an understatement.

So who invented the pan trap? I have of course given the name of the inventor away in the title of this article. They were invented surprisingly relatively recently, by the German entomologist Volker Moericke (Moericke, 1951), although I suspect that he used them some years before the publication of the paper. These first pan or Moericke traps as we should call them, were made of tin, painted yellow, and mounted on three wooden sticks. They were 22 cm in diameter and 6 cm deep and filled with a mixture of water and formaldehyde . Moericke was working on the aphid Myzus persicae . He was particularly interested in aphid vision and host location (Moericke, 1950). He observed that the aphids were able to distinguish between the red-yellow-green end of the spectrum and the blue-violet end. This then stimulated him to try trapping aphids using coloured pan traps (Moericke, 1951). He observed that the aphids were attracted to the yellow pan traps and behaved as if over a host plant resulting in them landing in the liquid from which they were unable to escape. Although he noted that the traps were extremely effective at catching aphids he did not comment on what other insects he found in the traps.

The first Moericke (yellow) Pan trap (from Moericke, 1951).

This simple, yet effective design has now become an essential part of the entomologist’s tool kit being used by field entomologists of every ilk working across the world in every habitat. They are truly an influential invention and worth of being named an entomological classic. Given the wide usage of these traps and their remarkable efficacy I think that we should make every effort to acknowledge their inventor by calling their modern plastic counterparts Moericke Traps.

Although I have recently written about my two years of blogging and tweeting, I couldn’t resist the temptation to begin 2015 with a quick round-up of 2014 on Don’t Forget the Roundabouts.

A gratuitous roundabout – collected summer 2014 Hook of Holland on our way back from our summer holiday.

According to the statistics provided by WordPress, I reached 145 countries (112 in 2013), and received about 24 000 views (14 349 in 2013).

Once again my most viewed post was Not All Aphids are Vegans with my post about saving UK plant sciences in second place. I continue to be surprised at how many people appear (or think that they have) to be bitten by aphids. In all my years of working with aphids I have only been probed (bitten, stung) twice. Looking at the distribution of hits for the post though it does seem to reflect the times of year when aphids are most active.

This post is obviously filling a need as the number of views has more than doubled since last year.

An innovation for 2014 was my series on entomological classics, mainly equipment, but I also included Southwood’s 1961 paper under that heading. This coming year I will continue much as before, posts about aphids, more entomological classics (look out for yellow water traps next), the odd rant or two and a new series on those scientific papers and authors that have really inspired me over the years.

I would really like to have more comments and interactions via the blog; at the moment Twitter is where most exchanges occur. It would also be nice if everyone who followed me on Twitter read my blog! That said I must acknowledge my most frequent commenters and bestowers of likes. These are Emily Scott http://adventuresinbeeland.com/, Jeff Ollerton http://jeffollerton.wordpress.com/, Amelia from A French Garden, and Emma Tennant http://missapismellifera.com/. I am also very grateful to the 135 people who subscribe to my blog. Many thanks to you all for your interest and kind words.

I write about politics, nature + the environment. Some posts are serious, some not. These are my views, I don't do any promotional stuff and these views are not being expressed for anyone who employs me.

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